1. Field of the Invention
The present invention relates to a spindle assembly which can be used as a component of an object transport system, i.e., a conveyor. More particularly, the present invention pertains to a spindle assembly that can be rapidly disassembled to allow cleaning and maintenance and can be rapidly reassembled with precise location of parts with respect to each other.
2. Description of the Related Art
A spindle assembly can be used as a component of an object transport system, e.g., an object carrying and rotating system, to carry an object through an operation or from one operation to another. A spindle assembly is able to rotate, allowing, for example, proper orientation of an object prior to an operation, orientation of an object during an operation, or continuous rotation of an object during an operation. For example, in the manufacture of certain plastic containers for food container applications, the containers are sprayed with a coating which inhibits the flow of oxygen into the interior of the container. Each container of a number of containers is placed onto a spindle assembly at a first station and is then transported by an object carrying and rotating system through a spray booth. The spindle assembly should allow each container to rotate in the spray booth to promote even distribution of the sprayed coating on the container. After exiting the spray booth, the containers continue to be transported to allow drying and/or cure of the coating on the container, either through exposure to the air under ambient conditions or through exposure to elevated temperatures in an oven. At a second station, each container is removed from the spindle assembly for further processing or for storage and shipping.
Previous spindle shaft assemblies have suffered from several limitations. For example, the spindle shaft assemblies presented in U.S. Pat. Nos. 4,927,205, 5,419,427, 5,558,200, and 5,769,476 all require removal of multiple parts in order to allow separation of the two sets of parts which rotate relative to each other. For example, in the spindle assembly presented in U.S. Pat. No. 5,419,427, a cap at the bottom of a spindle, labeled 46 in the patent document, must be unscrewed in order to access the hollow interior of the spindle 46 and the fastener 53 therein. The fastener 53 must then be unscrewed in order to separate the spindle 46 from the attachment pin 45. Such disassembly may be required at intervals in order to clean the interior of the spindle 46 and to clean the surfaces of the bushing 49 and the attachment pin 45 which move relative to each other during rotation. The need to remove or separate multiple parts in order to access and clean surfaces which move relative to each other, instead of needing to remove or separate only one part, results in an increase in disassembly time. Because a large number of spindle assemblies can be attached to a conveyor, the total increase in time for disassembly and cleaning or maintenance of all spindle assemblies can be substantial. Similarly, the need to reassemble multiple parts after cleaning or maintenance results in an increase in reassembly time. Furthermore, prior art spindle assemblies require an alignment procedure during reassembly to ensure that the proper clearance between parts which move relative to each other is established. Such an alignment procedure can be time consuming, require a skilled technician, and ultimately result in a poor alignment.
Because many spindle assemblies can be suspended from a conveyor, the total weight of the spindle assemblies must be considered in the design of and support for a conveyor. The additional support required for a conveyor carrying spindle assemblies can necessitate an increase in bulk and cost of a conveyor.
The large number of parts which constitute prior art spindle assemblies require a large number of replacement parts to be inventoried. The large number of parts in a spindle assembly increases the chances of improper interaction between the parts. For example, if there are a large number of parts which are screwed into another part, the chance of a thread in the assembly stripping is increased over the chance of a thread in an assembly having only a small number of screwed parts stripping.
In previous spindle assemblies, there is a large surface area between parts that move relative to each other with only small clearance between the parts. For example, in the spindle assembly presented in U.S. Pat. No. 5,769,476 the clearance is small between the surface of the shaft 54 and the surface of the bore of the spindle 56. The small clearance appears constant over the length of the shaft 54 which is located within the bore of the spindle 56. When parts of the spindle assembly rotate relative to each other, wear can occur leading to the production of debris. In prior art spindle assemblies that have a large surface area between parts with only small clearance to allow rotation, this debris and other residue, e.g., from a coating operation, can accumulate in the clearance space. Because the clearance is small, after a short period of time, sufficient debris and residue can accumulate in the clearance space and impede rotation or bind the parts such that they no longer can rotate relative to each other. Moreover, the debris and residue can result in increased friction which induces wear of the shaft and the spindle, leading to the production and accumulation of even more debris. For such previous spindle assemblies having a large surface area between parts that move relative to each other with only small clearance between the parts, binding resulting from accumulation of debris and residue can necessitate frequent disassembly and cleaning of the spindle assembly, with high costs associated with manufacturing downtime and labor.
Previous spindle assemblies have had problems with parts unscrewing, because of torque exerted between parts which rotate relative to each other. Such unscrewing can result in the sudden failure of a spindle assembly during operation.
There thus remains an unmet need for a spindle assembly that can operate for a long time before disassembly and cleaning is required, has a small number of constituent parts, can be rapidly and easily disassembled as required for maintenance and cleaning, can be rapidly and easily reassembled with a precise alignment of parts, with no alignment procedure required, and which does not have problems with sets of parts which move relative to each other unscrewing during operation.